invalid type argument of unary '*' (have double)

manpreet Best Answer 2 years ago

Just started learning c++ got this error:

C:\Users\KC\Documents\Math.cpp|9|error: invalid type argument of unary '*' (have 'double')|

This is the code:

#include 
#include 
#define M_PI
using namespace std;

int main()
{
   double area, radius = 1.5;
      area = M_PI * radius * radius;
   cout << area << "\n";
}

can someone explain to me what did I do wrong. Thanks

manpreet 2 years ago

#define M_PI

should be

#define M_PI 3.14159

(or whatever value you want to give for pi).

You defined M_PI as nothing, which means that this code

  area = M_PI * radius * radius;

becomes this code

  area = * radius * radius;

and your compiler is complaining about the unexpected *.